Seismic reliability evaluation of tunnel form (box‐type) RC structures under the accidental torsion

Abstract

In the tunnel form (box‐type) structural system, walls arrangement and mass distribution have important effect on the interactions of thinner shear walls and slab configurations. In the other words, despite the regularity of these buildings as well as symmetry in wall arrangement and mass distribution, the first mode of structural behavior in many cases is twisting. This characteristic is limited to the flexible torsional buildings, which are often sensitive to the mass eccentricity and rotational components of earthquake. According to the available guidelines for design and construction of tunnel form systems and emphasizing on regularity of these structural systems, it seems that the most probable mass irregularity of this type of structures is asymmetric distribution of live loads during service life. Therefore, in this paper, seismic behavior of box‐type (tunnel form) buildings is evaluated under the accidental torsion caused by asymmetric distribution of mass in stories. The incremental nonlinear dynamic analysis is used for this purpose. Despite the asymmetric distribution of mass in plan, the results demonstrate high capacity and appropriate seismic behavior of the tunnel form system. Therefore, an eccentricity equal to 10% of the plan dimension does not change the building performance level, which is higher than the immediate occupancy level under the design and maximum probable earthquake hazard levels.